The invention relates to a method for the overload protection of a mobile crane. Legal provisions require overload protection for all mobile cranes. In accordance with the standard EN 13000, which applies to the European Community, an overload protection is required for mobile cranes, for example, whose lifting capacity is greater than 1,000 kilograms or whose load moment is greater than 40,000 Nm. Mobile cranes are, for example, port mobile cranes, crawler-mounted cranes, etc.
It is already known to pre-calculate the cut-off curves required for the overload protection for all possible set-ups of the respective mobile crane and to store them in the memory of the overload protection. The cut-off curves are represented by a number of points which were calculated. Interpolation is carried out between these points in operation.
Since the stored curves require a lot of memory, interpolation is also frequently made between different load curves to save memory. The curve created in this way, however, no longer corresponds exactly to the results which would be received in a calculation with the calculation methods prescribed by the regulations. If the crane is now operated so that the appropriate values are exceeded in comparison with the cut-off curves calculated in accordance with the standard, this results in a relative loss of safety. If the real cut-off curves are not reached in this interpolation, the mobile crane is, however, not used to the optimum.
Mostly pre-calculated geometrical data are stored for each set-up for the calculation and display of load radius and, for example, crane height. A complete boom is here described, for example, in simplified manner by a vector. The current radius and other important information for the operator are then calculated by means of these data stored for the complete set-up by means of trigonometry and the data of position sensors. It was hoped that as few calculations as possible would have to be carried out using the method management.
If a mobile crane has only a few different set-ups, the known method, which makes use of the stored curves, can be used with comparatively few problems. It is though disadvantageous here that the behaviour of the crane (notably: inherent weight of the boom) must be adjusted in each case for each crane at the test rig of the mobile crane manufacturer since the component weights as a rule are not available in the accuracy required for the calculation of the overload protection.
Particularly with crawler-mounted cranes, unlike with other kinds of crane, the necessity exists to keep available a very high number of possible set-ups. With large cranes, several tens of thousands of set-ups can alternatively be reached. With the Liebherr crawler-mounted crane LR 1250, more than 20,000 set-ups result. It can be seen from this plurality of different combination possibilities that the memory for the load curves will be relatively large in the crane and under certain circumstances must be doubled when one single new set-up criterion is added.
To solve this problem, some manufacturers have introduced restrictions to the combination possibility of the crane components. This results in an unwanted reduced flexibility of the crane.
If a component is changed in the equipment of the crane, then the disadvantage exists in the known method that all load curves have to be recalculated which results in a new calculation of frequently several weeks. The same applies to the case that the crane operator required a set-up which was originally not provided. Problems also result in the conventional calculation methods in the development of mobile cranes, i.e. in the building of prototypes in which the component weights are not yet known so precisely in detail.
It is now the underlying object of the invention to provide a method for the overload protection of a mobile crane, in particular of a crawler-mounted crane, with which the respectively current cut-off values can be determined fast and precisely even with a plurality of possible set-ups.
This object is solved in accordance with the invention by a method for the overload protection of a mobile crane in accordance with
storage of component-related geometrical date in a memory (10);
selection of the desired set-up in a selection apparatus (16);
compilation of a physical stimulation model from the selected data in a control computer (18);
entry of real measurement data from force and position sensors (20) on the crane side;
calculation of first the geometrical data, center of gravity date and forces and subsequently the cut-off values; and
optionally, cut-off of the crane when the cut-off values are reached.
Unlike the prior art, overturning load curves are no longer stored in the memory associated with the control computer of the crane, but rather geometrical data with the physical properties of the components of the crane. With an appropriate selection of the desired set-up in a selection apparatus, the corresponding geometrical data, which correspond to the set-up, are then put together in a physical simulation model in the control computer. Now, the real measurement data from the force and position sensors on the crane side are determined and the geometrical data, the centre of gravity data and centre of gravity forces and subsequently the cut-off values are determined from these on the control computer. In the operation of the crane, this is then switched off as appropriate when a cut-off value is reached.
Preferred embodiments of the invention can be seen from the dependent claims following on from the main claim.
For instance, in a first preferred embodiment, the component-related geometrical data for each component type of the crane components are stored in associated geometrical files in the memory. Thus, no longer a complete boom is recorded, but the data of the boom sections and of the other component types are stored in geometrical files respectively associated with them. Here, one geometrical file each is required per component type. The instructions are stored in parallel in a corresponding crane configuration file according to which the crane components can be combined with one another. The different combination possibilities of the individual component types are recorded to form complete booms or set-up parts here.
In accordance with another preferred embodiment of the invention, a pre-selection possibility for the calculation of the cut-off values is also entered in the crane configuration file. The pre-selection possibilities in question are, for example, a calculation provision for permissible lifting loads in accordance with national law. For instance, the permissible lifting loads in the USA differ, for example, from those in Europe (in accordance with the standard EN 13000). On the basis of the method in accordance with the invention and the storage of the corresponding calculation provision, the result can be put together in modular form by accessing the respective data stored in the memory. According to the prior art, one was still forced to calculate a new, complete set of lifting load curves and to store it in the corresponding mobile crane for every different calculation provision, i.e. for example for every different legal order.
The values calculated in the control computer are advantageously reproduced in a display of a display apparatus. In the present method, not only the permissible lifting load and the corresponding limit curve can be displayed in this display apparatus, but simultaneously, more or less as a xe2x80x9cwaste productxe2x80x9d of the simulation model, the actual load, the radius, the crane height, etc.
Another advantageous embodiment of the invention consists of the set-up information being reproduced in the selection apparatus on a display apparatus for the operator. He can therefore put together the crane with the set-up as it is also put together in reality on the screen.